Projection systems for projecting color images are known from the prior art. As image sources, for example, computer-generated images or video sources are available. In this connection, different projection technologies are applied.
DE 43 26 899 A1 describes a projection system using three CRTs, one respectively for each of the three primary colors of red, green and blue, so as to generate color images. The images generated on the surfaces of each of said CRTs are respectively imaged onto a projection surface by an imaging optical system and superimposed there.
A viewer standing at a point where he can see the light exiting from the projector (which is already the case when viewing the projector from the side), recognizes three color surfaces, which are brighter or darker depending on the image content.
U.S. Pat. No. 5,321,499 A also describes a projection system comprising three CRTs, whose generated three partial images are superimposed by dichroic mirrors, such that only one optical system remains to effect imaging onto the projection surface.
The viewer standing between the projector and the projection surface can see a colored surface on the projector, said surface having a diameter of a few centimeters.
WO 96/12373 A1 uses a projection lamp cooperating with a transilluminated LCD matrix for image modulation in order to generate an image. The LCD matrix is in turn imaged onto the projection surface by an imaging optical system with an aperture whose size is in the order of a few centimeters.
EP 0 734 184 A2 describes a projection system which uses three LCD matrices operating in a reflection mode. This also requires projection optics complying with the laws of imaging, i.e. which have to be dimensioned with a suitably large diameter in order to provide images having a suitable light intensity.
U.S. Pat. No. 5,592,239 A describes a projection assembly using three reflecting mirror matrices for image modulation. In the same manner as in the already described projection methods, an imaging optical system is used for projection onto the projection surface, the free light exit of said system being in the order of between 5 cm and 10 cm.
An entirely different type of image-generation is described in DE 43 24 849 A1, wherein a projection method using a directly writing laser beam is used. In connection with this invention, such projector is referred to as a laser projector. The novel optical system described therein does not serve the purpose of enlarged imaging of an internal, small primary image, generated in the projector, but of increasing or decreasing the angles of deflection of the scanned laser beams in horizontal and vertical directions, which beams enter the optical system.
The technical demands made on the optical system for transforming the angle of deflection are essentially as follows: Angle magnification, depth of focus, geometric and chromatic errors of imaging, transmission. The size of the aperture of the angle transformation optics is typically also in the order of between 5 cm and 10 cm.
DE 195 22 698 A1 describes an optical system, wherein the variation of the angles of deflection can be effected in a continuous manner. In this case, a zoom function is provided with regard to the variation of the angles of deflection. Thus, the image size on the projection surface is variable. The opening of the angle transformation optics is greater than 5 cm in diameter also in this case.
When imaging charts onto an incident-light projection surface using one of the above-described projection systems, the projector is arranged relative to the viewer(s) such that the viewers will not be able to look directly into the imaging optical system. Scattered light exiting from the projector is not perceived and does not interfere with the perception of the image displayed.
Conditions are totally different for projection in a dome, wherein the projectors are arranged within the area of the dome serving as a projecting surface.
Such projection system is described in U.S. Pat. No. 3,687,530 A. Five projectors are arranged below an equatorial plane, each behind the spherical projection surface. Triangular windows are provided in the projection surface which crop the projected partial images such that they are combined on the projection surface to form a homogeneous large image.
U.S. Pat. No. 3,687,530 A remains silent on the size of the triangular opening. According to the laws of enlarging optical imaging and the cropping of the image provided here, however, the opening definitely has to be larger than the clear diameter of the projection optics in at least one direction.
In any case, it is possible here that the viewer may have one or more optical systems in his field of vision from his usual position. When light passes through optics, this will, in any case, generate scattered light, increased by particles of dust and dirt. Said scattered light has an interfering effect on viewing of the projected image. In particular, for image contents including night scenes, i.e. in flight simulation, astronomical projections and the like, such scattered light is found to strongly interfere. The more extensive the dimensions of the lenses are that can be perceived by the eye, the more interference will be caused by the scattered light.
It is the object of the invention to improve a projection arrangement wherein a viewer can perceive the projected light bundle exiting from the projector such that the interferences caused thereby in the perception of the image representation are reduced, if possible.
The object is achieved by an arrangement for projecting an image onto a projection surface, which image is composed of image points, said arrangement comprising at least one light source, which emits a light bundle and has a variable intensity; a deflection device, which deflects the light bundle onto the projection surface; and two-stage transformation optics, which are arranged between the deflection device and the projection surface and consist of two partial systems having positive power of refraction, and wherein the entrance pupil, as seen in the direction of light propagation, is located in front of the lens vertex of the transformation optics, and the exit pupil of the transformation optics is located between the lens vertex of the last lens of the transformation optics and the projection surface, and a stop is arranged in the exit pupil. The position of the exit pupil and the arrangement of the stop therein prevent a viewer from perceiving scattered light. The comparatively small stop aperture serves as a point of passage for the light bundle writing the image. Using the arrangement for projection according to the invention, the size of the light exit opening can be drastically reduced over the prior art. In particular, all scattering surfaces of the optical system for image projection can be arranged outside the field of vision of the viewer.
The solution according to the invention is applicable in any type of projection using a writing light bundle. A light source emitting laser radiation is particularly advantageous. Projectors using laser radiation are also known as laser projectors. Above all, the solution according to the invention provides advantages in those cases where the viewer, in order to view the projected image, has to look in the direction of the projector at the same time.
An advantageous embodiment of the invention consists in that the stop has a clear diameter, which corresponds to a diameter of the incident light bundle divided by an angular magnification of the transformation optics. In addition, a correction factor of between 1 and 1.5 should be considered, in order to safely and completely avoid cropping of the beam at the stop. It is essential that the diameter of the stop decrease proportionally at an angular magnification of >1. At an angular magnification of <1, the diameter of the stop increases proportionally compared to the diameter of the incident light bundle, with the stop aperture being considerably smaller also in these cases than the aperture of a lens according to the prior art. The viewer sees no optical surface and, thus, also no scattered light. As seen in the direction of light propagation, said stop is arranged following the last lens vertex of the transformation optics. Typically, the stop is arranged 1 cm to 50 cm posterior to the last lens vertex, so that nearly all constructional requirements for a projection system can be satisfied. In a different case, the stop can also be applied directly to the surface of the last optical surface of the transformation optics, as seen in the light direction.
In this case, the stop is part of a housing of the transformation optics. The lenses of the transformation optics are mounted within said housing. A mechanical connection to a biaxial deflection device is provided at one end of the housing. The other end of the housing is provided with the stop, which is the light exit for the deflected light bundle. In this case, the distance from the stop to the last lens vertex is advantageously less than 5 cm.
Another embodiment of the invention consists in that the stop is integrated into the surface of a wall and the transformation optics with the respective biaxial deflection device are positioned with respect to the stop in the wall. Thus, the position of the stop in the projection surface is designed such that a minimum possible diameter of the aperture in the projection screen is obtained.
A further embodiment of the invention consists in that one side of the wall forms the projection surface, that the projector with its transformation optics is arranged on an opposite side and the stop is incorporated into the projection surface. This arrangement is convenient, in particular, in a cylinder projection or in a dome projection. In most cases, the comparatively small stop aperture is not perceived at all or perceived only with great difficulty. The image information represented on the projection surface is distorted to the smallest possible extent.
In particular, the transformation optics can be corrected for imaging free from distortion. Depending on the particular application, such correction may be effected, for example, according to the tangential condition, which is described in more detail in DE 43 24 849 A1, or according to the angle condition. The correction according to the angle condition is particularly advantageous in projection onto a cylindrical or spherical projection surface. Thus, for example, in transformation optics for projection in a spherical surface, the transformation optics are embodied such that the entrance angle and the exit angle of the light bundle entering them and exiting from them, respectively, are directly proportional to one another. This means that, in projection from the center of a spherical dome, e.g. from the center of a planetarium, a Cartesian test pattern (chess board) can be projected without geometric distortion.
Further, an optical system for transforming the angle of an incident light bundle is provided, said system comprising two-stage transformation optics, which consist of two partial systems having positive power of refraction, said systems being arranged following each other in the direction of light propagation, wherein the ratio of the refractive powers of the partial systems determines the angular magnification of the deflected light bundle and the arrangement of the lenses in the second partial system is selected such that, as seen in the direction of light propagation, the exit pupil of the transformation optics is located between the lens vertex of the last lens of the transformation optics and the projection surface, and wherein a stop is arranged in the exit pupil. In combination with a stop in the exit pupil, this optical system or the transformation optics, respectively, provide the above-described advantages of the invention.
The optical system or the stop, respectively, may be further embodied in the same manner as in the arrangement according to the invention as described above.
The transformation optics may be corrected for imaging free from distortion. Again, such correction can be effected, for example, according to the tangential condition or according to the angle condition.
Further, an optical system for transforming the angle of an incident light bundle is provided, said system comprising two-stage optics for angle transformation, whose exit pupil is located within the lenses of the optical system, wherein relay optics consisting of two partial systems having positive power of refraction are arranged posterior to the angle transformation optics, as seen in the direction of light propagation, the arrangement of the lenses in the second partial system of the relay optics being selected such that, as seen in the direction of light propagation, an exit pupil of the relay optics is located between the lens vertex of the last lens of the relay optics and the projection surface, and wherein a stop is arranged in the exit pupil of the relay optics.
The relay optics do not change the amount of the angle of the light bundles entering them or exiting from them, but only change its mathematical sign (the original light being laterally inverted and upside down).
The use of the relay optics is particularly advantageous, if existing optics for angle transformation are combined with the relay optics and the stop, such that the above-described advantages of the invention and of its further embodiments are achieved by the combined system.
The two-stage angle transformation optics can be corrected for imaging free from distortion. Depending on the particular application, such correction may be effected, e.g., according to the tangential condition or according to the angle condition.
The optical system or the stop, respectively, may be further embodied in the same manner as in the arrangement according to the invention described above.